I kinda found the idea of an gigantic aqueduct strange and overkill - here is what came to my mind on reading the lore-stuff:

Das Tal is a canyon situated near the sea. It is difficult to access due to sheer cliffs. The river enters the canyon via waterfalls and exits it with very strong currents in multiple estuaries. Thus Das Tal is also inaccessible via the river or the sea. The most sensible way for easy access would be something like lifts or cablecars.

To make what we can do with the mapping easy and sensible: The river has carved the valley into different plateaus at different levels that are partially separated by chasms. Something causes highly different regions - the substance generating ice-energy, heat-energy, posion-energy, wind-energy, ... ? (Would need to visualize that a bit - the substance comes with spirits/ghosts in my imagination ...)

Another explanation would be a Canyon that stretches a large height span .. could be a Canyon meandering down a Mountainside. - would give a good, realistic linear structure to the map with options for wide areas, chokepoints and shortcuts ...

- Why are radically different biomes needed? There is no "whole planet" to fill...

A set of archetypical biomes might be very recognizeable, but are also a bit boring and like working down a checklist ...Wouldn't it be better to stick to a closer together set of biomes and make them more believable and fleshed out?

Right now the icy areas and the desert areas clash, there are intermediate regions needed - climate could be neighbouring, since the desert could be a cool arid area... saw some earlier rocks from the icy area in the art thread that would fit in an intermediate region - or just apply the biome shader to more props for intermediaries...